Axial piston pump

ABSTRACT

A pump comprises a rotary cylinder block which contains a number of axially reciprocating pistons and the axis of rotation of which is inclined to the axis of rotation of a driving shaft of the pump; the cylinder block is driven by the driving shaft through bevel gears having a 1:1 ratio. The cylinder block rotates in bearings in a pump housing and the pistons are connected to a driving flange on the driving shaft by connecting rods which extend between universal joints at their ends. Each cylinder is connected through a port in the cylinder wall to an inlet duct during substantially half of each revolution of the cylinder block and to an outlet duct during substantially the remaining part of each revolution. The inlet and outlet ducts are situated on opposite sides of the plane which contains the axes of rotation of both the cylinder block and the driving shaft. The bearings in which the cylinder block rotates extend around the periphery of the cylinder block and the bevel gears are external, the driving bevel gear extending around the periphery of the driving flange and the driven bevel gear extending around the periphery of the cylinder block. The ports are directed outwards from the cylinders towards inlet and outlet ducts arranged between the cylinder block and the internal peripheral wall of the housing and these ducts connect with further inlet and outlet ducts through the housing itself.

[451 May8,1973

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tains a number of axially reciprocating pistons and the axis of rotation of which is inclined to the axis of rotation of a driving shaft of the pump; the cylinder block is driven by the driving shaft through bevel gears having a 1:1 ratio. The cylinder block rotates in bearings cylinder wall to an inlet duct during substantially half of each revolution of the cylinder block and to an outlet duct during substantially the remaining part of each revolution. The inlet and outlet ducts are situ- A pump comprises a rotary cylinder block which conin a pump housing and the pistons are connected to a driving flange on the driving shaft by connecting rods which extend between universal joints at their ends. Each cylinder is connected through a port in the ated on opposite sides of the plan-e which contains the block 6 Ciaims,9l)ra wing Figures outlet ducts arranged between the cylinder block and the internal peripheral wall of the housing and these ducts connect with further inlet and outlet ducts through the housing itself.

United States Patent [191 Chivari [54] AXIAL PISTON PUMP Ilie Chivari, Von-der-Recke-Strasse 19, Bochum, Germany [75 Inventor:

[73] Assignee: valkahkupplmig's-u. cane-655i Bernhard Hackforth, Wanne-Eickel, Germany [22'] Filed? 16;"1'970 211 Appl.No.: 18,183

Foreign Application Priority Data Mar 13,1969 Germany....................

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AXIAL PISTON PUMP The invention relates to pumps of the kind which comprise a rotary cylinder block which contains a number of' axially reciprocating pistons and the axis of rotation of which is inclined to the axis of a driving shaft of the pump, the cylinder block being driven by thedriving shaft through 1:1 bevel gear wheels. The cylinder block rotates in bearings in a pump housing and the pistons are connected to a driving flange on the driving shaft by connecting rods which extend between universal joints at their ends. Each cylinder is connected through a port in the cylinder wall to an inlet duct during substantially half of each revolution of the cylinder block, and to an outlet duct during substantially the remaining part of each revolution. The inlet and outlet ducts are situated on opposite sides of the plane which contains the axes of rotation of both the cylinder block and the driving shaft. Such pumps are subsequently referred to as of the kind described.

Pumps of the kind described, which can also be used as hydraulic motors, compare favorably with axial piston pumps of the swash plate kind in which the cylinder block is stationary, the cylinder block and the driving shaft are coaxial and the pistons are reciprocated by a rotating swashplate, the pistons or rods fixed to the pistons being held in contact with the surface of the swashplate by springs.

In pumps of the kind described the connection of the pistons to the driving shaft through universally jointed connecting rods provides the advantage firstly that the friction which occurs at the surface of a swashplate in pumps of the swashplate kind is avoided. Secondly the angle between the axes of the cylinder block and the driving shaft may be greater than the angle of skew of y the swashplate thus giving a longer piston stroke for a given radius. The angle of skew between the plane of a swashplate and the driving shaft axis has a practical limit beyond which friction at the surface of the swashplatebecomes too great.

In the known pumps of the kind described, the angle between the driving shaft axis and the cylinder block axis is however also limited to 45 at the most because the bevel gearing for transmitting the drive from the driving shaft to the cylinder block is situated centrally between the cylinder block and the driving flange of the driving shaft, that is to say between the connecting rods. A further disadvantage of the known pumps of the kind described is that the cylinder block must be of large diameter, because it rotates on a stationary central axle in which the inlet and outlet ducts are formed. The radial cylinder ports open inwards, connecting inwardly with the inlet and outlet ducts, which consequently have cross-sections considerably smaller than those of the cylinders. The small cross-sections of these ducts limit any improvement in efficiency which might otherwise be obtained by increasing the stroke lengths of the pistons.

The object of the present invention is to increase the output of a pump of the kind described by inclining the cylinder block at a greater angle with respect to the driving shaft than has previously been possible, and to improve the efficiency of the pump by increasing the cross-sections of the inlet and outlet ducts to obtain total duct cross-sectional areas as nearly as possible equal to the total cylinder cross-sectional areas of the aspirating and delivering cylinders.

To this end, according to this invention, in a pump of the kind described the cylinder block rotates in the pump housing in bearings extending around the periphery of the cylinder block, the bevel gear wheels are external, the driving bevel gear wheel extending around the periphery of the driving flange and the driven bevel gear wheel extending around the periphery of the cylinder block and the ports are directed outwards from the cylinders towards an inlet and an outlet in the housing through inletand outlet ducts situated between the cylinder block and the internal peripheral wall of the housing.

In a pump constructed in this way the angle between the axis of rotation of the cylinder block and the axis of the driving shaft is no longer limited by the presence of the central bevel gear wheels. The angle can be nearly 90, being limited only by the requirement that the connecting rods and their joints on the driving flange must not interfere with each others movements. The outwardly directed radial ports in the walls of the cylinders, and the inlet and outlet situated in between the cylinder block and the housing and in the housing make it possible to give these passages the best possible crosssections. A further advantage is that, in spite of the increased output and improved efficiency of the pump the entire assembly may be made considerably more compact, and the masses of the rotating parts may be reduced.

In spite of the fact that the cylinders are grouped closely together in a comparatively small cylinder block, the performance of the pump in accordance with the invention, particularly in view of the longer piston stroke which is possible is comparable with the performances of much larger and heavier pumps and motors of conventional type.

An example and a modification of the example, of a pump constructed in accordance with the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a longitudinal section through the pump taken in the common plane containing the axis of the cylinder block and the axis of the driving shaft;

FIG. 2 is a cross-section through the cylinder block and housing taken on the line AA in FIG. 1;

FIG. 3 is an axial section through the cylinder block and the housing taken on the line B-B in FIG. 2;

FIG. 4 is a cross-section taken on the line CC in FIG. 5 is a cross-section taken on the line D-D in FIG. 3;

FIG. 6 is an axial section through the driving flange, showing the parts mounted on the flange;

FIG. 7 is a cross-section taken on the line E-E in FIG. 6;

FIG. 8 is an axial section similar to part of FIG. 1, but showing the modification; and,

FIG. 8a is a plan view showing; a driving bevel gear wheel forming part of the modification.

In the example shown in FIGS. 1 to 7, a housing part 1 contains a cylinder block 9 and a housing part 3 contains a driving shaft 30. The axis of the cylinder block 9 is inclined at an angle of relative to the axis of the driving shaft 30. The two housing parts 1 and 3 are connected together by a hollow angular connecting housing part 2, the three housing parts being tightly jointed together.

The housing part 2 encloses a chamber 31 which contains oil introduced through a filling opening 32 which can be closed by a closure.

The cylinder block 9 is everywhere circular in cross section and rotates in the housing part 1 on a lower roller bearing 10 and an upper grooved ball bearing 11, the cylinder block 9 is located axially by a roller thrust bearing 14.

As will be seen from FIG. 2, the cylinder block 9 contains five bored cylinders 13, each containing a pump piston 12. The upper end of each cylinder 13 is sealed by a plug 15 which has pressure tight ring seals 16. The plugs 15 are secured by screws 17 to the under surface of a cover plate 9a which covers the upper end of the cylinder block 9. The cover plate 94 is secured to the cylinder block 9 by a central screw 19 and by further screws 18 which can be seen in FIG. 4. The central screw 19 has an axial bore 190 connecting a central lubricant channel 9b of the cylinder block 9 to the gap between the cylinder block cover plate 9a and an oil tight outer housing cover plate 1a. Each cylinder 13 has an upper radial port 130 situated in the cylinder wall above the working face of the piston when the piston is in its highest position. The port 130 connects the cylinder to an annular chamber situated between the cylinder block 9 and the peripheral wall of the housing part 1. The annular chamber contains a tightly fitting guide ring 4, which is prevented from rotating in the housing part 1 by a screw 20 the inner end of which engages in an axial groove in the guide ring 4. The guide ring 4 has two substantially semi-circular passages separated from each other by diametrically opposite bridges 4a as shown in FIG. 2. Each passage consists of an approximately semi-circular outer groove 5, 6 and an approximately semi-circular inner groove 5a, 6a, the outer and inner grooves being connected together by passages 5b, 6b, which pass through a separating wall 4c. The separating wall 40 serves for stiffening the guide ring 4, which would otherwise be weakened too much by the passages extending over its entire cross section. The diametrically opposite bridges 4a are at the level of the cylinder ports so that with the rotation of the cylinder block 9 the two passages 7, 8 passing through the wall of the housing part 1 and connecting to the two outer annular grooves 5, 6 of the guide ring 4 act as inlet and outlet ducts. These two passages 7, 8 are connected in the usual way to inlet and delivery pipes for the pump, which are not shown in the drawings.

Each one of a number of connecting rods 27 is connected to a piston 12 by a universal ball joint 12a, the other end of each connecting rod being connected to a driving flange 30a of the drive shaft 30 by a universal joint. Each of these universal joints consists, in this example, of a bearing 28 mounted on a pivoted pin 29 which is rotatable in a bevel gear wheel 33 fixed to the driving flange 300 so that the pin 29 can rotate about an axis parallel to that of the driving shaft. Each pivoted pin 29 is free to rotate in a roller bearing 34, the pin 29 being located axially by a grooved ball bearing 35. Each ball bearing 35 is mounted in a ring 36 secured tightly between the driving flange 30a and the bevel gear wheel 33. The bevel gear wheel 33 has peripheral palloid teeth 33a which mesh with similar teeth 19 on a flange 9c of the cylinder block 9. The

bevel wheel 33 and the ball bearing ring 36 are attached to the driving flange 30a by a central screw 37 and by further screws 38 shown in FIGS. 6 and 8.

The driving shaft 30 rotates in the housing part 3 in an upper roller bearing 39 and two lower grooved ball bearings 40, 41 which locate the driving shaft 30 axially in both directions in the housing-part 3. The grooved ball bearings 40, 41 are themselves located axially relative to the housing part 3 and to the driving shaft 30, by annular collars and spring circlips.

The manner in which the pump functions will be understood best from FIGS. 1 and 3. In FIG. 1 one of the two pistons 12 shown is at top dead center the other is at bottom dead center. However in the case of a pump which has an uneven number of cylinders, as represented in the drawing, these two extreme piston positions cannot in reality occur simultaneously. A piston reaches upper dead center as it rotates past one of the bridges 4a of the guide ring 4, the cylinder port being at this instant blocked by the bridge 4a. Let us assume that the cylinder block is rotating counterclockwise, as seen looking down on the top of the cylinder block through the cover plate 9a. This direction of rotation is represented in FIG. 2 by an arrow. When a cylinder port is blocked by the upper bridge 4a the upper piston is at bottom dead center and the lower piston is at top dead center. With further rotation of the cylinder block liquid is therefore sucked in from the left through the inlet passage 7 and expelled towards the right through the outlet passage 8, as indicated by the small arrows in FIG. 2. FIG. 3 shows two pistons in their middle positions, the left hand piston being halfway through its downward suction stroke and, the right hand piston halfway through its upward delivery stroke. These two piston positions cannot however occur simultaneously in a pump with an uneven number of cylinders.

In order to prevent unbalanced pressures on the cylinder block, that is to say different pressures on either side of the axial plane containing the two bridges 4a, the inner surface of the guide ring 4 has, above and below the grooves 5a, 6a further grooves 21, 22 on one side and 23, 24 on the other side (see, FIG. 3) the further grooves 21, 22 and 23, 24 having the same lengths as the grooves 5a, 6a. Pressure relief channels 25, 26 (see FIG. '5) cut into the guide ring 4 connect the grooves situated on one side of the axial plane containing the bridges 4a to the passages 6, 6a, 6b and 5, 5a, 5b.on the other side. The pressure relief channels 25, 26 largely balance out pressure differences acting asymetrically on the cylinder block.

In the examples shown in FIGS. 1 to 6, the bearings 34 for the pivot pins 29 are installed directly in the bevel wheel 33. This makes it necessary to use a bevel gear wheel of large diameter, to give room for the bearings 34 and 35, which must be accommodated in the level wheel 33 having the bevel teeth 33a, to operate. The other bevel wheel 9c on the cylinder block 9 must also have the same large diameter. The modification shown in FIGS. 8 and 8a, allows bevel gear wheels of smaller diameter to be used. In this modification the roller bearings 34 for the pivot pins 29 are installed in a bearing ring 36 mounted on the bevel wheel 33, which itself holds the grooved ball bearings 35 for the pivot pins 29. The bevel wheel 33' is clamped tightly between the ring 36' and the driving flange a of the driving shaft.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

lclaim:

1. In a pump of the type having a cylinder block and means for rotatably supporting said cylinder block for rotation about a first axis, mean's defining a plurality of cylinders in said cylinder block, a drive shaft rotatably mounted in said pump about a second axis, bevel gear means connecting said cylinder block and said drive shaft, a stationary housing in which said means for rotatably supporting said cylinder block are arranged, a plurality of pistons reciprocably mounted in said plurality of cylinders, a plurality of connecting rods, universal joint means operatively connecting, on the one hand, said plurality of connecting rods to said plurality of pistons and, on the other hand, to said drive shaft, means defining a plurality of inlet and outlet ports in said cylinder block, each one of said ports communicating with one of said cylinders, means defining an inlet duct, means defining an outlet duct and means communicating a number of said ports with said inlet duct during substantially half of each revolution of said cylinder block and communicating said ports with said outlet duct during substantially the other half of each revolution of said cylinder block, said inlet duct and said outlet duct being arranged on opposite sides of a plane containing said first and second axes, the improvement, comprising in combination,

a double jointed universal joint forming part of said universal joint means and connecting said rods to said drive shaft via said bevel gear means;

said inlet and outlet ports being radially disposed with respect to said first axis and having a total cross-sectional area which is substantially equal to the total cross-sectional area of said cylinders;

said inlet duct and outlet duct having a total crosssectional area which is substantially equal to the total cross-sectional area of said plurality of inlet and outlet ports;

said first and second axes making an angle larger than 45 therebetween; and

means defining further inlet and outlet ducts which include a guide ring; and

means mounting said guide ring between said cylinder block and said housing, said means mounting said guide ring including separating bridges extending from said guide ring to said housing and separating said further inlet duct from said further outlet duct;

the effective cross-sectional areas of said further inlet and outlet ducts are arranged in a guide ring forming part of said defining means and the effective cross-sectional areas of said inlet and said outlet ducts which are disposed in said housing are at least as great as the sum of the cross-sectional areas of said ports which are in communication with said inlet and said outlet ducts at any instant during the rotation of said cylinder block; said guide ring includes means defining grooves above and grooves below said passages through said ring, said grooves having the same peripheral extents as said passages, and means defining pressure balance passages in said guide ring through said bridges communicating those of said grooves above and below said inlet passages with those of said grooves above and below said outlet passages.

2. A pump as claimed in claim 11, wherein said further inlet duct and said further outlet duct each comprise means defining a substantially semi-circular groove between said guide ring and said housing, means defining an inner substantially circular groove between said guide ring and said cylinder block, and means defining passages through said guide ring, said passages communicating said substantially semi-circular groove with said substantially circular groove.

3. A pump as claimed in claim 1, including means fixing said bevel gear means comprise a driving flange, a peripheral flange means forming part of said driven bevel means.

4. A pump as claimed in claim 1, wherein said universal joint means are connected to one end of each of said connecting rods and includes bearing means fixed to said bevel gear means, a pivot pin mounted in said bearing means for rotation about an axis parallel to said axis of said driving shaft and further bearing means mounted on said pivot pin, said further bearing means allowing said connecting rod to turn about an axis at right angles to said axis of said driving shaft.

5. A pump as claimed in claim 4, comprising means mounting said pivot pin in said driving bevel gear means, said bevel gear means comprise a bevel gear wheel and a driving flange fixedly mounted thereon, a bearing ring interposed between said driving flange and said driving bevel gear wheel and grooved ball bearing means mounted in said bearing ring, said grooved ball bearing means locating said pivot pin in the axial direction thereof;

6. A pump as claimed in claim 5, further comprising an annular disc, means fixing said annular disc to said driving flange, means mounting said pivot pin in said annular disc, means clamping said bevel gear wheel between said annular disc and said driving flange and grooved ball bearing means mounted in said annular disc, said grooved ball bearing means locating said pivot pin in the axial direction thereof. 

1. In a pump of the type having a cylinder block and means for rotatably supporting said cylinder block for rotation about a first axis, means defining a plurality of cylinders in said cylinder block, a drive shaft rotatably mounted in said pump about a second axis, bevel gear means connecting said cylinder block and said drive shaft, a stationary housing in which said means for rotatably supporting said cylinder block are arranged, a plurality of pistons reciprocably mounted in said plurality of cylinders, a plurality of connecting rods, universal joint means operatively connecting, on the one hand, said plurality of connecting rods to said plurality of pistons and, on the other hand, to said drive shaft, means defining a plurality of inlet and outlet ports in said cylinder block, each one of said ports communicating with one of said cylinders, means defining an inlet duct, means defining an outlet duct and means communicating a number of said ports with said inlet duct during substantially half of each revolution of said cylinder block and communicating said ports with said outlet duct during substantially the other half of each revolution of said cylinder block, said inlet duct and said outlet duct being arranged on opposite sides of a plane containing said first and second axes, the improvement, comprising in combination, a double jointed universal joint forming part of said universal joint means and connecting said rods to said drive shaft via said bevel gear means; said inlet and outlet ports being radially disposed with respect to said first axis and having a total cross-sectional area which is substantially equal to the total cross-sectional area of said cylinders; said inlet duct and outlet duct having a total cross-sectional area which is substantially equal to the total cross-sectional area of said plurality of inlet and outlet ports; said first and second axes making an angle larger than 45* therebetween; and means defining further inlet and outlet ducts which include a guide ring; and means mounting said guide ring between said cylinder block and said housing, said means mounting said guide ring including separating bridges extending from said guide ring to said housing and separating said further inlet duct from said further outlet duct; the effective cross-sectional areas of said further inlet and outlet ducts are arranged in a guide ring forming part of said defining means and the effective cross-sectional areas of said inlet and said outlet ducts which are disposed in said housing are at least as great as the sum of the cross-sectional areas of said ports which are in communication with said inlet and said outlet ducts at any instant during the rotation of said cylinder block; said guide ring includes means defining grooves above and grooves below said passages through said ring, said grooves having the same peripheral extents as said passages, and means defining pressure balance passages in said guide ring through said bridges communicating those of said grooves above and below said inlet passages with those of said grooves above and below said outlet passages.
 2. A pump as claimed in claim 1, wherein said further inlet duct and said further outlet duct each comprise means defining a substantially semi-circular groove between said guide ring and said housing, means defining an inner substantially circular groove between said guide ring and said cylinder block, and means defining passages through said guide ring, said passages communicating said substantially semi-circular groove with said substantially circular groove.
 3. A pump as claimed in claim 1, including means fixing said bevel gear means comprise a driving flange, a peripheral flange means forming part of said driven bevel means.
 4. A pump as claimed in claim 1, wherein said universal joint means are connected to one end of each of said connecting rods and includes bearing means fixed to said bevel gear means, a pivot pin mounted in said bearing means for rotation about an axis parallel to said axis of said driving shaft and further bearing means mounted on said pivot pin, said further bearing means allowing said connecting rod to turn about an axis at right angles to said axis of said driving shaft.
 5. A pump as claimed in claim 4, comprising means mounting said pivot pin in said driving bevel gear means, said bevel gear means comprise a bevel gear wheel and a driving flange fixedly mounted thereon, a bearing ring interposed between said driving flange and said driving bevel gear wheel and grooved ball bearing means mounted in said bearing ring, said grooved ball bearing means locating said pivot pin in the axial direction thereof.
 6. A pump as claimed in claim 5, further comprising an annular disc, means fixing said annular disc to said driving flange, means mounting said pivot pin in said annular disc, means clamping said bevel gear wheel between said annular disc and said driving flange and grooved ball bearing means mounted in said annular disc, said grooved ball bearing means locating said pivot pin in the axial direction thereof. 